In preventing or extinguishing fires, two important elements must be considered for success: (1) separating the combustibles from air; and (2) avoiding or reducing the temperature necessary for combustion to proceed. Thus, one can smother small fires with blankets or with foams to cover the burning surfaces to isolate the combustibles from the oxygen in the air. In the customary process of pouring water on the burning surfaces to put out the fire, the main element is reducing temperature to a point where combustion cannot proceed. Obviously, some smothering or separation of combustibles from air also occurs in the water situation.
The particular process used to extinguish fires depends upon several items, e.g. the location of the fire, the combustibles involved, the size of the fire, etc. In fixed enclosures such as computer rooms, storage vaults, rare book library rooms, petroleum pipeline pumping stations and the like, halogenated hydrocarbon fire extinguishing agents are currently preferred. These halogenated hydrocarbon fire extinguishing agents are not only effective for such fires, but also cause little, if any, damage to the room or its contents. This contrasts to the well-known "water damage" that can sometimes exceed the fire damage when the customary water pouring process is used.
The halogenated hydrocarbon fire extinguishing agents that are currently most popular are the bromine-containing halocarbons, e.g. bromotrifluoromethane (CF.sub.3 Br, Halon 1301) and bromochlorodifluoromethane (CF.sub.2 ClBr, Halon 1211). It is believed that these bromine-containing fire extinguishing agents are highly effective in extinguishing fires in progress because, at the elevated temperatures involved in the combustion, these compounds decompose to form products containing bromine atoms which effectively interfere with the self-sustaining free radical combustion process and, thereby, extinguish the fire. These bromine-containing halocarbons may be dispensed from portable equipment or from an automatic room flooding system activated by a fire detector.
In many situations, enclosed spaces are involved. Thus, fires may occur in industrial or nuclear power plant control rooms, in military vehicles, and like areas where continuous human occupancy is almost mandatory. It is important that the fire extinguishing agents that are used continue to permit safe human occupancy in the enclosed space, despite their use.
The use of an effective amount of fire extinguishing agent in an atmosphere which would also permit human occupancy in the enclosed space involves two situations. In one situation, the fire extinguishing agent is introduced into the enclosed space to extinguish an existing fire; the second situation is to provide an ever-present atmosphere containing the fire "extinguishing" or, more accurably prevention agent in such an amount that fire cannot be initiated nor sustained. Thus, in U.S. Pat. No. 3,844,354, Larsen suggests the use of chloropentafluoroethane (CF.sub.3 --CF.sub.2 Cl) in a total flooding system (TFS) to extinguish fires in a fixed enclosure, the chloropentafluoroethane being introduced into the fixed enclosure to maintain its concentration at less than 15%. On the other hand, in U.S. Pat. No. 3,715,438 Huggett discloses creating an atmosphere in a fixed enclosure which is habitable but, at the same time, does not sustain combustion. Huggett provides an atmosphere consisting essentially of air, a perfluorocarbon selected from carbon tetrafluoride, hexafluoroethane, octafluoropropane and mixtures thereof and make-up oxygen, as required.
It has also been known that bromine-containing halocarbons such as Halon 1301 can be used to provide a habitable atmosphere that will not support combustion. However, the high cost due to bromine content and the toxicity to humans i.e. cardiac sensitization at relatively low levels (e.g. Halon 1301 cannot be used above 7.5-10%) make the bromine-containing materials unattractive for long term use.
In recent years, even more serious objections to the use of brominated halocarbon fire extinguishants has arisen. The depletion of the stratospheric ozone layer, and particularly the role of chlorofluorocarbons (CFC's) have led to great interest in developing alternative refrigerants, solvents, blowing agents, etc. It is now believed that bromine-containing halocarbons such as Halon 1301 and Halon 1211 are at least as active as chlorofluorocarbons in the ozone layer depletion process.
While perfluorocarbons such as those suggested by Huggett, cited above, are believed not to have as much effect upon the ozone depletion process as chlorofluorocarbons, their extraordinarily high stability makes them suspect in another environmental area, that of "greenhouse effect". This effect is caused by accumulation of gases that provide a shield against heat transfer and results in the undesirable warming of the earth's surface.
There is, therefore, a need for an effective fire extinguishing composition and process which can also provide safe human habitation and which composition contributes little or nothing to the stratospheric ozone depletion process or to the "greenhouse effect".
It is an object of the present invention to provide such a fire extinguishing composition; and to provide a process for preventing and controlling fire in a fixed enclosure by introducing into said fixed enclosure, an effective amount of the composition.